Accuracy and axilla sparing potentials of sentinel lymph node biopsy with methylene blue alone performed before versus after neoadjuvant chemotherapy in breast cancer: a single institution experience

The timing of sentinel lymph node biopsy (SLNB) of breast cancer in the neoadjuvant setting is still controversial. We retrospectively analyzed a Chinese patient cohort with neoadjuvant chemotherapy (NAC) to evaluate the accuracy and axilla sparing potentials of different SLNB timings with methylene blue alone for lymphatic mapping.Patients with NAC and axillary lymph node dissection (ALND) and either pre- or post-NAC SLNB were eligible. Clinicopathological characteristics, identification rate (IR), false-negative rate (FNR), accuracy, and positive-predictive value were calculated and compared between the pre- and post-NAC SLNB group using appropriate statistical methods. Axilla sparing potentials of different SLNB timings were evaluated and compared.One hundred and fifteen eligible cases were included, and 58 had pre-NAC SLNB while the other 57 had post-NAC SLNB. Both groups were comparable in clinicopathological characteristics, neoadjuvant treatments and pathologic complete response rate. IR, FNR, and accuracy of SLNB, as pre-NAC versus post-NAC, were 100 versus 98.2 % (P = 0.496), 0 versus 8.0 % (P = 0.181), and 100 versus 96.4 % (P = 0.239), respectively. Post-NAC SLNB had significantly higher positive-predictive value for ALNs than pre-NAC SLNB (70.0 vs. 36.4 %, P = 0.014), suggesting as high as 63.6 % of ALND performed in the pre-NAC group could have been avoided while only 30 % of ALND in the post-NAC group were theoretically unnecessary.Both SLNB timings of breast cancer patients with NAC were feasible and accurate. Although pre-NAC SLNB tends to be better in accuracy, post-NAC SLNB is significantly superior in terms of axilla sparing.